This invention relates generally to a fire extinguishing sprinkler valve and, more particularly, to an on-off fire extinguishing sprinkler valve.
One type of known on-off sprinkler head employs a temperature responsive actuator to control the pressure in a pilot volume disposed on one side of a piston valve and communicating with a water supply applying pressure to the opposite side of the valve. In response to variations in ambient temperature the pressure in the pilot volume changes relative to the supply pressure and thereby causes desired opening and closing operation of the valve. Examples of pilot volume actuated on-off sprinkler heads are disclosed in U.S. Pat. Nos. 3,702,160; 3,746,098; 3,748,176; 3,757,866 and 4,359,098. Individual and collective disadvantages of pilot volume valves include structural complexity, leak prone movable seals, dependence on differential pressure actuation, etc.
Another type of on-off sprinkler head employs a temperature responsive actuator such as a wax motor to directly operate a flow valve. Examples of directly operated sprinkler heads are disclosed in U.S. Pat. Nos. 3,734,191; 3,802,510 and 3,911,940. Disadvantages of directly actuated heads include a requirement for spring members to effect valve closures and a relatively slow response of the direct actuators. The latter deficiency can be obviated by a sprinkler head disclosed in U.S. Pat. No. 3,924,687 and which used a conventional fusible link actuated straight on valve in series with a directly actuated on-off sprinkler valve. By selecting a melting temperature for the fusible link that is higher than the actuation temperature of the direct actuator, the on-off valve can be made to positively and completely open prior to opening of the straight-on valve. The sprinkler head disclosed in U.S. Pat. No. 3,924,687 exhibits the cost and complexity disadvantages inherent in a head employing two distinct valves.